1. Field of the Invention
The present invention generally relates to a four-color liquid crystal display, and more particularly, to a structure of a pixel of transreflective liquid crystal display adopting a rendering method and a four-color technology.
2. Description of the Related Art
Liquid crystal displays (LCDs) are among the most widely used flat panel display devices. Generally, an LCD includes a pair of panels each having an electrode on an inner surface, and a dielectric anisotropic liquid crystal layer interposed between the panels. In the LCD, the variation of the voltage difference between the field generating electrodes, e.g., the variation in the strength of an electric field generated by the electrodes, changes the transmittance of the light passing through the LCD, and thus desired images are obtained by controlling the voltage difference between the electrodes.
Depending on a type of light source used for image display, an LCD may be classified as three types: a transmissive LCD, a reflective LCD, and a transreflective LCD. The transmissive LCD includes pixels that are illuminated from a back side using a backlight. The reflective LCD includes pixels that are illuminated from a front side using incident light of the ambient environment. The transreflective LCD combines the transmissive and the reflective characteristics. Under medium light conditions such as an indoor environment or under complete darkness conditions, transreflective LCDs operate in the transmissive mode, while under bright conditions such as in an outdoor environment, transreflective LCDs operate in the reflective mode.
A four-color subpixel technology, in which a white subpixel is added to a set of red, green, and blue subpixels, has been developed to improve the brightness of LCD panels.
The four-color technology controls a resolution of an LCD by a rendering method. In the subpixel rendering method, red, green, blue, and white subpixels are individually controlled. When a specific subpixel operates, the subpixels adjacent thereto operate along with the specific pixel, so that a pixel is represented as the brightness divided by the specific pixel and the adjacent operating subpixels. With this method, more specific expressions of slant lines or curved lines become possible, improving the resolution.
In the LCDs adopting such a subpixel rendering technology, a set of six subpixels, rather than a set of four subpixels form one pixel. In this structure, red, green, blue, and white subpixels are arranged substantially in a matrix. For example, red-blue-green subpixels may be arranged in an upper horizontal line and green-white-red subpixels may be arranged in a lower horizontal line.
Conventionally, the four-color rendering technology has only been applicable to the reflective LCDs, no transmissive LCD currently uses this technology.
When applying the rendering technology to the existing transflective LCDs having reflective areas and transmissive areas, chromaticity coordinates of white are transferred, generating a yellowish phenomenon.
In conventional LCDs, the ratio of a transmissive area and a reflective area assigned in each subpixel is approximately 2:1, and the brightness ratio of the transmissive areas or the reflective areas for the red, green, blue, and white subpixels is 2:2:1:1. The yellowish phenomenon is caused by an insufficient blue component. To compensate for such a component, a method compensating the blue component of lamps that supply light to the LCD may be used. However, this method is applicable to the transmissive mode, and is not applicable to the reflective mode because the reflective mode utilizes natural light.